In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Dental restoration parts can be manufactured from ceramic or plastic shaped bodies. This procedure is usually mechanical, for example, computer-aided according to a CAD/CAM method. With regard to the final use of the dental restoration parts, the shaped bodies should already have certain aesthetic properties.
Natural teeth are not one-colored, but have a complex coloration. Different areas of the same tooth can differ from each other in color and transparency. In general, teeth exhibit a color and transparency gradient from transparent in the occlusal area to yellowish-opaque in the cervical area.
In order to achieve a desired coloration, dental restoration parts which have a single color can be subsequently veneered. However, such veneering usually has to be carried out manually, which is time-consuming. Multi-colored shaped bodies are therefore preferred from which dental restoration parts can be manufactured that satisfy aesthetic requirements without veneering and which have a coloration that comes as close as possible to natural teeth in terms of color and transparency, as well as color gradient.
Multi-colored shaped bodies which are built up from several differently colored layers are known from the state of the art.
Thus, VITA Zahnfabrik GmbH offers VITABLOCS® Triluxe, which consist of three differently colored layers of a feldspar ceramic and are intended to simplify the manufacture of optically attractive dental restoration parts. These restoration parts are, however, still veneered.
U.S. Pat. No. 5,151,044 describes multi-layered blocks made from plastic materials which can be used for the manufacture of artificial teeth or denture parts. These blocks preferably contain up to three differently colored layers in order to simulate the color gradient of natural teeth.
Furthermore, it is known from DE 199 44 130 A1 to use blocks comprising several differently colored layers with standardized optical properties for the manufacture of denture parts by means of CAD/CAM methods. In doing so, the virtual positioning of the restoration part within a block is optimized such that the color gradient of what later becomes the restoration part comes as close as possible to a corresponding natural tooth of the patient. Veneering of the restoration parts produced in this way is said to be dispensable.
However, in the case of the multi-colored shaped bodies which are built up of differently colored layers, the color boundaries between the individual layers are clearly perceptible. Therefore the restoration parts produced according to the state of the art must be veneered as previously mentioned in order to achieve a restoration satisfying high aesthetic requirements.
DE 197 14 178 A1 describes a process for manufacturing a multi-colored shaped body wherein the color boundaries between the individual layers are said not to be perceptible. According to this, the contact surfaces of the individual layers are subjected to pressure and the differently colored starting materials are brought into intimate contact in the boundary area to allow for a mixing of the starting materials.
However, practice has shown that this process does not lead to an adequate mixing and therefore the boundaries between the colored layers in the thus-produced shaped bodies and restoration parts remain perceptible to the naked eye.
There is therefore a need for a multi-colored shaped body for producing dental restorations with differently colored layers in which no color boundaries can be seen with the naked eye between the individual layers.